C语言实现内存相关操作函数（memset、memcmp、memcpy、memmove）

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#include <stdio.h>
#include <string.h>
#include <assert.h>
//memset函数
void* my_memset(void* ptr, int value, size_t num)
{
	//参数有效性检查
	assert(ptr != NULL);
	char* tptr = (char*)ptr;
	//初始化内存
	while (num-- != 0)
	{
		*tptr++ = value;
	}
	return ptr;
}
int main()
{
	int ar[10];
	my_memset(ar, 0, sizeof(int) * 10);
	for (int i = 0; i < 10; ++i)
	{
		printf("%d ", ar[i]);
	}
	printf("n");
	return 0;
}

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#include <stdio.h>
#include <string.h>
#include <assert.h>
//memcmp函数
int my_memcmp(const void* ptr1, const void* ptr2, size_t num)
{
	//参数有效性检查
	assert(ptr1 != NULL && ptr2 != NULL);
	//保护参数
	const char* tptr1 = (char*)ptr1;
	const char* tptr2 = (char*)ptr2;
	int ret = 0;
	//比较
	while (num-- != 0)
	{
		ret = *tptr1 - *tptr2;
		if (ret != 0)
		{
			break;
		}
		tptr1++;
		tptr2++;
	}
	return ret;
}
int main()
{
	char* ar = "hello";
	char* br = "hella";
	int flag = my_memcmp(ar, br, sizeof(char) * 5);
	printf("flag = %d", flag);
	return 0;
}

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#include <stdio.h>
#include <string.h>
#include <assert.h>
//memcpy函数
void* my_memcpy(void* dest, const void* src, size_t num)
{
	//参数有效性检查
	assert(dest != NULL && src != NULL);
	//保护参数
    char* pdest = (char*)dest;
    const char* psrc = (const char*)src;
	//对内存中的内容进行拷贝
	while (num-- != 0)
	{
		*pdest++ = *psrc++;
	}
	return dest;
}
int main()
{
	int ar[10] = { 0,1,2,3,4,5,6,7,8,9 };
	int br[10];
	my_memcpy(br, ar, sizeof(int) * 10);
	for (int i = 0; i < 10; ++i)
	{
	    printf("%d ", br[i]);
	}
	return 0;
}

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#include <stdio.h>
#include <string.h>
#include <assert.h>
//memmove函数
void* my_memmove(void* dest, const void* src, size_t num)
{
	//参数有效性检查
	assert(dest != NULL && src != NULL);
	//保护参数
	char* pdest = (char*)dest;
	const char* psrc = (const char*)src;
	//对内存中的内容进行拷贝
	if (psrc >= pdest || pdest >= psrc + num)
	{
		while (num-- != 0)
		{
			*pdest++ = *psrc++;
		}
	}
	//如果发生内存重叠，则从后往前拷贝内存中的内容
	else
	{
		pdest = pdest + num - 1;
		psrc = psrc + num - 1;
		while (num-- != 0)
		{
			*pdest-- = *psrc--;
		}
	}
	return dest;
}
int main()
{
	char str1[20] = "abcdefghi";
	char str2[] = "ABCDEF";
	printf("str1 = %sn", str1);
	printf("str2 = %sn", str2);
	my_memmove(str1, str2, 6);
	printf("str1 = %sn", str1);
	my_memmove(str1 + 2, str1, 5);
	printf("str1 = %sn", str1);
	return 0;
}